There may be several reasons:
- Open Event Viewer and look for errors related to user profile loading under "Windows Logs" -> "System". The error messages might provide clues about the root cause.
- Large roaming profiles can cause delays. So, consider reducing the profile size.
- If the profile seems corrupted, try resetting it.
https://techcommunity.microsoft.com/t5/windows-10/roaming-profile-not-synchronizing/m-p/2799188